Perforated laminate sheets are used in a variety of application including Helmholtz resonators which include a honeycomb core supporting a perforated laminate face sheet. Such structures are used to form the arcuate inner surfaces of the nose cowl and thrust reverser components of a nacelle system of a commercial jet aircraft.
Surprisingly, perforating a composite laminate is not a straight forward process. The problems with drilling, abrasion, stamping, water jet, laser beam, and other similar processes are documented in U.S. Pat. Nos. 5,268,055 and 5,252,279 incorporated herein by this reference.
So, these and other patents (e.g., U.S. Pat. Nos. 4,541,879; 4,390,584; 5,419,865; 4,612,737; and 4,486,372) delineate a different perforation methodology wherein a pin mat is used to perforate the composite laminate. The pin mat is formed from a plate with a number of interconnected, integral, upstanding pins or studs. A number of these pin mats are interlocked and a laminate, usually in the prepreg stage, is driven onto the pin mat using pressure or some kind of an impacting tool.
The primary limitation with this manufacturing method is the extremely high number of man hours required to fabricate the pin mats, assemble them on a forming tool, form the perforated composite laminate sheet, and to then re-work the perforations due to the fact that a number of pins usually break off from the pin mat during processing. Another limitation is that since the pins of the pin mat must be extracted from the perforated laminate in the same direction they were inserted, the pins must have a conical shape resulting in tapered perforations which are not as beneficial as straight perforations. Moreover, extruded pin mats, typically only available in 27".times.43" sheets, require heat treating and theremoforming before use.